Behavior of female Rhyzopertha dominica (Coleoptera: Bostrichidae) in a mono-layer of wheat treated with diatomaceous earth

Adult female lesser grain borers (Rhyzopertha dominica [F.]) were observed in a mono-layer of wheat sandwiched between two layers of glass to determine if movement patterns and survival rates differed in wheat that was admixed with diatomaceous earth (DE) compared with untreated wheat. Observations were also made to determine if responses to DE differed depending on the commercial formulation of DE tested at the labeled rates. Mortality was higher in the DE treatments than in the untreated controls, and also varied according to the DE formulation. In wheat treated with 1000 ppm Dryacide®, 400 ppm Protect-It®, and 500 ppm Insecto™ (labeled rate for the individual products), mean percentage mortality was 100±0, 71.4±10.1, and 57.1±11.1, respectively. Although total distance traveled and the number of turns taken by the beetles was lower in the Dryacide treatment compared to the untreated controls, the movement patterns were not significantly different among the three DE treatments. Observed differences in mortality are likely related to DE products or amount applied rather than to differences in DE exposure resulting from movement behavior.